A portable device becomes lighter and smaller according to development of electronic technology, and accordingly, requires a smaller and lighter high performance rechargeable battery with high energy characteristics as an energy source. As for the rechargeable battery, a rechargeable lithium battery has a high voltage of 3V or higher and high energy density, and thus has been paid the most attention to.
This rechargeable lithium battery consists of positive and negative electrodes, an electrolyte, a separator, an exterior material, and the like. The positive electrode may include a lithium transition element compound such as LiCoO2, LiMn2O4, LiNiO2, LiMnO2, and the like as a positive active material.
As for a negative active material, carbon has been widely used, but a lithium titanate negative active material with better safety and very small irreversible capacity has been recently paid more attention to. This lithium titanate has an operation voltage ranging from 1.3 to 1.6 V, and thus almost no irreversible reaction, and also has excellent safety due to very low reaction heat compared with a conventional carbon-based negative active material. In addition, while a carbon negative active material has a low theoretical density of about 2 g/cc, lithium titanate has a high theoretical density of 3.5 g/cc and thus high energy density per volume. Accordingly, lithium titanate has recently drawn attention as an alternative for a conventional carbon negative active material in order to be applied to a medium- or large-sized rechargeable lithium battery for an electric vehicle or an electric power storage system.
This lithium titanate may be prepared by using titanium dioxide (TiO2) as a starting material. Recently, in order to improve properties of a lithium titanate negative active material, titanium dioxide itself, a starting material of the lithium titanate, has been researched regarding improving properties.